Kinetics and cyclability of limestone (CaCO3) in presence of steam during calcination in the CaL scheme for thermochemical energy storage

Abstract

In the present work, we explore the use of steam in the CaCO3 calcination step of a calcium looping process devised for integration into a thermochemical energy storage process (CaL-TCES). Steam produces a double benefit: firstly, it fastens the calcination, allowing a reduction of the temperature needed to attain full calcination in short residence times, as those required in practice, resulting in energy savings. This behaviour is justified on the bases of kinetic study results, as obtained from a non-parametric kinetic analysis, which demonstrates that the presence of steam during calcination can reduce the apparent activation energy from 175 kJ/mol to 142 kJ/mol with a steam’s partial pressure of 29%. In addition, the results obtained for multicycle CaL-TCES tests show that steam alleviates the deactivation of the sorbent, which is one of the main limiting factors of this technology. This behaviour is explained in terms of the effect of steam on the microstructure of the resulting CaO. Importantly, the values of the residual conversion attained calcining in steam are higher than those without steam.